How do you figure out what is actually wrong with a transmission?

Summary:

Jaden walks through the shop's diagnostic sequence in order. It starts with a road test, where he drives the vehicle specifically looking for the symptoms the customer described. After the test drive he scans the vehicle and reads codes. Next he checks the fluid, noting both level and condition, and he calls out color as a key indicator, contrasting bright pink fluid against brown. The final step, used often, is pulling the transmission pan. He explains why that step matters: anything that fails inside a transmission ends up in the bottom of the pan, so dropping it provides a direct look at the condition of the internals. He is careful to say it is not every time, but usually if something is failing badly there will be visible evidence in the pan, whether clutch material, metal, or other debris.

Answer:

So when the car first comes in, I'm going to test drive it and look for the symptoms that the customer explains. And then I'll get back from the test drive and then I'll scan it and look for codes. And then I will check the fluid, see what the fluid looks like, if it's full, if it's low, if it's nice and bright pink or if it's brown. Another thing that we do often is we'll pull the pan on the transmission, and dropping the pan of the transmission will give us a glimpse inside the transmission, because anything that fails winds up in the bottom. And so usually, I mean, not every time, but usually if something's failing pretty badly, we'll see evidence of it in the pan, whether that be clutch material or metal or whatever. So between the road test, the codes, the fluid, and what's sitting in that pan, we get a pretty good picture of what's going on inside before we ever pull the unit out.